This research mainly involves the analysis of long-term serial data (0-60 years) concerning subcutaneous fat thickness and estimates of total body fat in human beings. Almost all the data to be analyzed have been collected in the major growth studies that will cooperate in this work and they have been put into a rapid retrieval format. These data will be supplemented by others obtained from additional examinations of Fels participants. Fat biopsy data for the Fels participants will provide fat cell size. The underwater weight will allow the calculation of fat cell number (if cell size is known) and total body fat. This independent measure of total body fat will allow an assessment of the validity of indirect measures, such as those based on weight and height. Further validation studies will be based on estimates of total body fat from K40, water displacement, air displacement and D2O. Blood triglycerides and cholesterol will help estimate the health significance of different levels and patterns of body fat. The major objectives are to establish the "normal" pattern of fat deposition and loss for the age range 0-60 years and, in addition: to determine the predictors of obesity in childhood and at older ages; to determine the causation (familial, genetic, etc.) and significance (illness experience) of obesity in infancy and at other ages; to analyse the relationships between subcutaneous fat thickness and rate of maturation; to provide equations that estimate total body fat from anthropometric variables.